Hole transport polymers and devices made with such polymers

ABSTRACT

The present invention is generally directed to a hole transport polymer comprising a polymeric backbone having linked thereto a plurality of substituents comprising fused aromatic ring groups, with the proviso that the polymer does not contain groups selected from triarylamines and carbazole groups. It further relates to devices that are made with the polymer.

This application claims priority to provisional application, Ser. No.60/369,663, filed Apr.2, 2002 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to polymeric materials having useful holetransport properties. The polymers can also be electroluminescent. Theinvention further relates to electronic devices in which the activelayer includes such polymeric materials.

2. Description of the Related Art

Organic electronic devices that emit light, such as light-emittingdiodes that make up displays, are present in many different kinds ofelectronic equipment. In such devices, an organic active layer issandwiched between two electrical contact layers. At least one of theelectrical contact layers is light-transmitting so that light can passthrough the electrical contact layer. The organic active layer emitslight through the light-transmitting electrical contact layer uponapplication of electricity across the electrical contact layers.

It is well known to use organic electroluminescent compounds as theactive component in light-emitting diodes. Simple organic molecules suchas anthracene, thiadiazole derivatives, and coumarin derivatives areknown to show electroluminescence. Semiconductive conjugated polymershave also been used as electroluminescent components. Polymericmaterials with stilbenyl or oxadiazole side chains have been reported byHolmes et al., U.S. Pat. No. 5,653,914.

Many electroluminescent materials have poor charge transport properties.To improve these properties additional charge transport materials can beadded to the light-emitting layer, or as a separate layer between thelight-emitting layer and an electrode. Hole transport materials havefrequently been employed. Known hole transport materials include simplemolecules such asN,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD) andbis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP),and polymeric materials such as polyvinylcarbazole (PVK),(phenylmethyl)polysilane, poly(3,4-ethylenedioxythiophene) (PEDOT), andpolyaniline (PANI). It is also known to use electron and holetransporting materials such as 4,4′-N,N′-dicarbazole biphenyl (BCP); orlight-emitting materials with good electron and hole transportproperties, such as chelated oxinoid compounds, such astris(8-hydroxyquinolato)aluminum (Alq₃). Fused aromatic ring compoundssuch as pentacene are known to be electron transport materials.Copolymers having two different pendant aromatic groups have beendisclosed as light-emitting materials in U.S. Pat. No. 6,007,928.

There is a continuing need for new hole transport materials.

SUMMARY OF THE INVENTION

The present invention is directed to a hole transport polymer includinga polymeric backbone having linked thereto a plurality of substituentsthat includes at least one fused aromatic ring group, with the provisothat the polymer does not contain groups selected from triarylamines andcarbazole groups.

The invention is further directed to an organic electronic device havingan active layer between an anode and a cathode, wherein the devicefurther has at least one first hole transport polymer that includes apolymeric backbone having linked thereto a plurality of substituentsincluding at least one fused aromatic ring group, with the proviso thatthe polymer does not contain groups selected from triarylamines andcarbazole groups.

As used herein, the term “hole transport material” is intended to meanmaterial that can receive a positive charge from the anode and move itthrough the thickness of the material with relatively high efficiencyand small loss. The term “hole transport polymer” is intended to meanpolymeric hole transport material. The term “polymer” is intended toinclude homopolymers as well as copolymers having two or more differentrepeating units. The term “functionalized polymer” is intended to mean apolymer having at least one functional group(s) capable of reacting toattach a fused aromatic ring group to the polymer backbone. The term“functionalized fused aromatic ring compound” is intended to mean afused aromatic ring compound having at least one functional group(s)capable of reacting to attach to the polymer backbone. The term“photoactive” refers to any material that exhibits electroluminescenceand/or photosensitivity. The term “(meth)acrylic” is intended to meanacrylic, methacrylic or combinations. The term “(meth)acrylate” isintended to mean acrylate, methacrylate, or combinations. In addition,the IUPAC numbering system is used throughout, where the groups from thePeriodic Table are numbered from left to right as 1 through 18 (CRCHandbook of Chemistry and Physics, 81^(st) Edition, 2000).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a light-emitting device (LED).

FIG. 2 is a current vs voltage curve for the device of Example 5.

FIG. 3 is a current vs voltage curve and a light-emission vs voltagecurve for the device of Example 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The at least one fused aromatic ring group of the substituents attachedto the polymeric backbone generally has from 10 to 50 carbon atoms andcontain from 2 to 8 fused aromatic rings, preferably 2 to 4. The fusedaromatic ring group can optionally be substituted with alkyl or arylgroups having 1 to 20 carbon atoms. Examples of suitable fused aromaticring groups include naphthyl, anthracyl, phenanthryl, phenalenyl,fluorenyl, pyrenyl, and other tetracenyl and pentacenyl groups. Inaccordance to the present invention, hole transport properties areachieved in the absence of groups which are generally used to providehole transport properties, such as triarylamine groups and carbazolegroups.

The hole transport polymers can be obtained by reacting a polymer havinga first type of reactive group (“functionalized polymer”) with a fusedaromatic ring compound having a second type of reactive group(“functionalized fused aromatic ring compound”). This is shownschematically in Reaction (1) below.Pol-R¹+Ar-R²=Pol-R³-Ar+(S)   Reaction (1)where Pol represents the polymeric backbone, Ar represents the fusedaromatic ring, R¹ and R² represent the first type and second type ofreactive groups, respectively, R³ represents the linkage resulting fromthe reaction of R¹ and R^(2,), and S represents any byproducts which maybe formed in the reaction.

Techniques for attaching small molecules to polymers are well-known, asin the coupling of biochemical ligands to latex particles. This isdiscussed in, for example, Uniform Latex Particles, by L. B. Bangs (Form#1661–84 from Seragen Diagnostics, Inc., Indianapolis, Ind., 1984). Forexample, a polymer having carboxylic acid functional groups can bereacted with a fused aromatic ring compound having amino functionalgroups, forming an amide linkage. Alternatively, the carboxylic acidgroup can be on the fused aromatic ring and the amino group on thepolymer. Similarly, hydroxyl groups react with acid chloride groups toform ester linkages. Other types of reactive pairs include hydroxyl andchloromethyl groups; hydroxyl and carboxylic acid groups; isocyanate andhydroxyl or amine groups; epoxy and amine groups; acid chloride andamine groups; sulfonic acid and amine groups; sulfonic acid chloride andhydroxyl groups; aldehyde and amino groups; aldehyde and carboxylgroups; aldehyde and hydroxyl groups; and aldehyde and methylketonegroups. A variety of reactions that will provide linkages are availablein the synthetic organic chemistry literature.

Alternatively, the hole transport polymer can be obtained bypolymerizing at least one type of monomer having attached thereto afused aromatic ring group (“functionalized monomer”), as shown inReaction (2) below.Mon-R⁴-Ar→Pol-R⁴-Ar   Reaction (2)where Mon represents a polymerizable compound, R⁴ represents a linkinggroup, and Ar and Pol are as defined in Reaction (1) above.I. Functionalized Polymer

The functionalized polymeric compounds that are useful in the presentinvention can be generally described as having: (a) a polymericbackbone; (b) a plurality of a first-type functional group; optionally(c) a spacer group between the polymeric backbone and the first-typefunctional group; and optionally (d) a plurality of second-typefunctional group(s) that are the same or different from each other. Thepolymeric backbone can be any polymer or copolymer having the desiredproperties and processability, and to which the fused aromatic ringgroups can be attached. Some categories of useful polymeric backbonesinclude polyacrylates; polymethacrylates; polyaramids; polystyrenes;polyarylenes; polyvinylenes; polyvinyl ethers; and polyvinyl esters.

The first-type functional groups useful for attaching the fused aromaticring groups, are any of those discussed above as part of a reactivepair.

The number of fused aromatic groups on the polymeric backbone, whichalso can be described as the “density of fused aromatic groups”, willaffect the efficiency of the polymer as a hole transport material.However, when choosing the polymer, other factors should also be takeninto consideration, such as processability and film forming capability.For the polymeric materials of the invention, the density of fusedaromatic groups is determined by the relative proportion of monomershaving first-type functional groups (“first-type functional monomers”)to other monomers not having first-type functional groups in thepolymer. In general, the ratio of first functional monomers to othermonomers can be in the range of about 5:95 to 95:5.

The first-type functional group can be attached directly to the polymerbackbone, as, for example, the carboxyl group of a polyacrylic acidpolymer. However, it is also possible to have a spacer group between thefirst-type functional group and the polymeric backbone. Useful spacergroups are those that are chemically stable and do not deleteriouslyaffect the transport properties of the polymer. The spacer group can bea saturated or unsaturated aliphatic group, or an aromatic group. Thespacer group can contain heteroatoms, particularly oxygen and nitrogen.In some cases, a spacer group is present because the most readilyavailable monomers for certain first functional groups have the spacergroup. The spacer group generally has from 1 to 50 carbon atoms;preferably from 5 to 15 carbon atoms. The spacer group can simplyprovide distance between the polymer backbone and first functionalgroup, or it can provide functionality, as discussed below.

The functionalized polymer can also have at least one second-typefunctional group. The second-type functional group can be present tomodify the physical properties of the final polymer. Examples of suchtypes of groups include plasticizing groups, such as alkylene oxidegroups, and reactive and/or crosslinkable groups, such as terminal vinylgroups and epoxy groups. The second-type functional group can be presentin the polymer backbone, in the spacer group attached to the first-typefunctional group, or in pendant groups separate from the first-typefunctional group.

The functionalized polymer can be made using monomer(s) having thedesired functional group(s), using conventional polymerizationtechniques. Examples of suitable monomers include (meth)acrylic acid(carboxyl functionality); 4-styrenecarboxylic acid (carboxylfunctionality); aminoalkyl acrylates and methacrylates (aminofunctionality); hydroxylalkyl (meth)acrylates (hydroxy funcationality);glycidyl (meth)acrylate (epoxy functionality); and similar monomershaving the desired functional group.

The functionalized polymers can be a homopolymer or a copolymer. Thecopolymers can be prepared so that they are random, alternating, block,or comb copolymers. The process for forming these different structuralcopolymers are well known in the art, and have been discussed in, forexample, Principles Of Polymerization, 3rd Edition, by George Odian(John Wiley & Sons, New York, N.Y., 1991); Chemical Reactions of Naturaland Synthetic Polymers, by M. Lazar et al.; and Chemical Reactions onPolymers, by Benham and Kinstle (1988).

II. Functionalized Fused Aromatic Ring Compounds

Functionalized fused aromatic ring compounds have reactive groupscapable of reacting with groups on the functionalized polymer, asdiscussed above. Useful types of functionalized fused aromatic ringcompounds include aromatic amines, aromatic sulfonyl chlorides, aromaticisothiocyanates, aromatic succinimidyl esters, aromatic aldehydes, andaromatic alcohols or phenols. Some of these compounds are commerciallyavailable, such as 1-(1-naphthyl)ethylamine; 1-pyrenemethylamine;1-pyrenepropylamine; 4′-(aminomethyl)fluorescein; rhodamine B ethylenediamine; rhodamine B sulfonyl chloride; and5-dimethylaminonaphthylene-1-sulfonyl chloride. Other suitablefunctionalized fused aromatic ring compounds can be prepared usingstandard synthetic chemical techniques.

III. Functionalized Monomers

In general, functionalized monomers can be prepared by coupling thefunctional groups to monomers, using the same coupling chemistry asdescribed above. When the hole transport polymer is prepared fromfunctionalized monomers it is possible to get more structurallywell-defined polymeric materials. The functionalized monomers can bepolymerized using processes that result in different structures, such asblock copolymers, alternating copolymers, comb polymers, and other knownpolymeric structures. When the hole transport polymer is prepared from afunctionalized polymer and functionalized fused aromatic ring compound,the reactions occur in a more random, statistically controlled manner.

IV. Devices

The present invention also relates to an electronic device comprising anorganic active layer sandwiched between two electrical contact layers,an anode and a cathode, wherein the device further comprises the holetransport polymer of the invention. A typical structure is shown inFIG. 1. The device 100 has an anode layer 110 and a cathode layer 150.Adjacent to the anode is an optional layer 120 comprising a holetransport material. Adjacent to the cathode is an optional layer 140comprising an electron transport material. Between the anode and thecathode (or the optional charge transport layers) is the organic activelayer 130. The hole transport polymer of the invention is present in theorganic active layer 130, and/or in the hole transport layer 120. It isunderstood that each functional layer may be made up of more than onelayer.

The device generally also includes a support, which can be adjacent tothe anode or the cathode. Most frequently, the support is adjacent theanode. The support can be flexible or rigid, organic or inorganic.Generally, glass or flexible organic films are used as a support.

The anode 110 is an electrode that is particularly efficient forinjecting or collecting positive charge carriers. It can be made of, forexample materials containing a metal, mixed metal, alloy, metal oxide ormixed-metal oxide, or it can be a conducting polymer. Suitable metalsinclude the Group 11 metals, the metals in Groups 4, 5, and 6, and theGroups 8–10 transition metals, as shown on the periodic table ofelements (current IUPAC format). If the anode is to belight-transmitting, mixed-metal oxides of Groups 2, 3, 4, 13 and 14metals, such as indium-tin-oxide. A conducting polymer, such aspoly(3,4-ethylenedioxythiophene) (PEDOT), and polyaniline (PANI) can beused when the conductivity is greater than 10⁻² S/cm. At least one ofthe anode and cathode should be at least partially transparent to allowthe passage of light into or out from the active layer of the device.

Inorganic anode layers are usually applied by a physical vapordeposition process. The term “physical vapor deposition” refers tovarious deposition approaches carried out in vacuo. Thus, for example,physical vapor deposition includes all forms of sputtering, includingion beam sputtering, as well as all forms of vapor deposition such ase-beam evaporation. A specific form of physical vapor deposition whichis useful is rf magnetron sputtering. The conductive polymer anodelayers can be applied using any conventional means, includingspin-coating, casting, and printing, such as gravure printing, ink jetprinting or thermal patterning.

The hole transport polymer of the invention can be present as a separatelayer 120, or in combination with the emitting material in layer 130.The polymer layer can be applied using any conventional applicationmeans, as described above. The polymer is generally applied as asolution or dispersion in organic solvents such as dimethyl sulfoxide,N-methyl pyrrolidone, dimethyl formamide, acetonitrile, propylenecarbonate, propylene glycol monomethyl ether, dimethyl acetamide, andtetrahydrofuran. The concentration of the polymer in the solvent is notparticularly critical, so long as the solution or dispersion can becoated to form a continuous film. In general, solutions or dispersionhaving 1 to 5% by weight of the polymer can be used.

In some cases it may be desirable to have an additional hole transportlayer (not shown) made from other hole transport materials. Examples ofother suitable hole transport materials for layer have been summarizedfor example, in Kirk-Othmer Encyclopedia of Chemical Technology, FourthEdition, Vol. 18, p. 837–860, 1996, by Y. Wang. Both hole transportingmolecules and polymers can be used. Commonly used hole transportingmolecules are:N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD); 1,1-bis[(di-4-tolylamino) phenyl]cyclohexane (TAPC);N,N′-bis(4-methylphenyl)-N,N′-bis(4-ethylphenyl)-[1,1′-(3,3′-dimethyl)biphenyl]-4,4′-diamine(ETPD); tetrakis-(3-methylphenyl)-N,N,N′, N′-2,5-phenylenediamine (PDA);α-phenyl-4-N,N-diphenylaminostyrene (TPS); p-(diethylamino)benzaldehydediphenylhydrazone (DEH); triphenylamine (TPA);bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane (MPMP);1-phenyl-3-[p-(diethylamino)styryl]-5-[p-(diethylamino)phenyl]pyrazoline(PPR or DEASP); 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB);N,N,N′,N′-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TTB);and porphyrinic compounds, such as copper phthalocyanine. Commonly usedhole transporting polymers are polyvinylcarbazole (PVK) and(phenylmethyl)polysilane. Conductive polymers such aspoly(3,4-ethylenedioxythiophene) (PEDOT), and polyaniline (PANI), can beused when the conductivity is below 10⁻² S/cm. It is also possible toobtain hole transporting polymers by doping hole transporting moleculessuch as those mentioned above into polymers such as polystyrene andpolycarbonate. These materials can be applied by conventional coating orvapor deposition techniques.

In many cases, the anode and the hole transport layer are patterned. Itis understood that the pattern may vary as desired. The layers can beapplied in a pattern by, for example, positioning a patterned mask orphotoresist on the first flexible composite barrier structure prior toapplying the first electrical contact layer material. Alternatively, thelayers can be applied as an overall layer and subsequently patternedusing, for example, a photoresist and wet chemical etching. As discussedabove, the conductive polymer layer can also be applied in a pattern byink jet printing, lithography, screen printing, or thermal transferpatterning. Other processes for patterning that are well known in theart can also be used.

Depending upon the application of the device 100, the active layer 130can be a light-emitting layer that is activated by an applied voltage(such as in a light-emitting diode or an illumination device), a layerof material that responds to radiant energy and generates a signal withor without an applied bias voltage (such as in a photodetector), or alayer that converts radiant energy into electrical energy, such as aphotovoltaic cell or solar cell. Examples of electrical devices includephotoconductive cells, photoresistors, photoswitches, phototransistors,and phototubes, and photovoltaic cells, as these terms are describe inMarkus, John, Electronics and Nucleonics Dictionary, 470 and 476(McGraw-Hill, Inc. 1966).

Where the active layer is light-emitting, the layer will emit light whensufficient bias voltage is applied to the electrical contact layers. Thelight-emitting active layer may contain any organic electroluminescentor other organic light-emitting materials. Such materials can be smallmolecule materials such as those described in, for example, Tang, U.S.Pat. No. 4,356,429, Van Slyke et al., U.S. Pat. No. 4,539,507, therelevant portions of which are incorporated herein by reference. Thelight-emitting materials can be organo-metallic complexes, as describedin, for example, published US application US 2001/0019782 and publishedPCT applications WO 00/70655 and WO 01/41512. Alternatively, suchmaterials can be polymeric materials such as those described in Friendet al. (U.S. Pat. No. 5,247,190), Heeger et al. (U.S. Pat. No.5,408,109), Nakano et al. (U.S. Pat. No. 5,317,169), the relevantportions of which are incorporated herein by reference. Preferredelectroluminescent materials are semiconductive conjugated polymers. Anexample of such a polymer is poly(p-phenylenevinylene) referred to asPPV.

The light-emitting materials may form a layer alone, or they may bedispersed in a matrix of another material, or may be combined with thehole transport polymer of the invention. The concentration of the chargetransport material has to be above the percolation threshold ofapproximately 15 volume %, such that a conducting pathway can beestablished. When the density of the material is close to one, 15 wt %is acceptable as long as the percolation threshold is reached. The holetransport polymer of the invention is generally present in an amount ofabout 15 to 99% by weight, based on the total weight of the emittinglayer, preferably 25 to 80% by weight.

The active organic layer generally has a thickness in the range of50–500 nm.

Where the active layer is incorporated in a photodetector, the layerresponds to radiant energy and produces a signal either with or withouta biased voltage. Materials that respond to radiant energy and iscapable of generating a signal with a biased voltage (such as in thecase of a photoconductive cells, photoresistors, photoswitches,phototransistors, phototubes) include, for example, many conjugatedpolymers and electroluminescent materials. Materials that respond toradiant energy and is capable of generating a signal without a biasedvoltage (such as in the case of a photoconductive cell or a photovoltaiccell) include materials that chemically react to light and therebygenerate a signal. Such light-sensitive chemically reactive materialsinclude for example, many conjugated polymers and electro- andphoto-luminescent materials. Specific examples include, but are notlimited to, MEH-PPV (“Optocoupler made from semiconducting polymers”, G.Yu, K. Pakbaz, and A. J. Heeger, Journal of Electronic Materials, Vol.23, pp 925–928 (1994); and MEH-PPV Composites with CN-PPV (“EfficientPhotodiodes from Interpenetrating Polymer Networks”, J. J. M. Halls etal. (Cambridge group) Nature Vol. 376, pp. 498–500, 1995).

The active layer 130 containing the active organic material can beapplied from solutions by any conventional means, includingspin-coating, casting, and printing. The active organic materials can beapplied directly by vapor deposition processes, depending upon thenature of the materials. It is also possible to apply an active polymerprecursor and then convert to the polymer, typically by heating.

The cathode 150 is an electrode that is particularly efficient forinjecting or collecting electrons or negative charge carriers. Thecathode can be any metal or nonmetal having a lower work function thanthe first electrical contact layer (in this case, an anode). Materialsfor the second electrical contact layer can be selected from alkalimetals of Group 1 (e.g., Li, Cs), the Group 2 (alkaline earth) metals,the Group 12 metals, the rare earths, the lanthanides, and theactinides. Materials such as aluminum, indium, calcium, barium, andmagnesium, as well as combinations, can be used. Li-containingorganometallic compounds can also be deposited between the organic layerand the cathode layer to lower the operating voltage.

The cathode layer is usually applied by a physical vapor depositionprocess. In general, the cathode layer will be patterned, as discussedabove in reference to the anode layer 110 and conductive polymer layer120. Similar processing techniques can be used to pattern the cathodelayer.

Optional layer 140 can function both to facilitate electron transport,and also serve as a buffer layer or confinement layer to preventquenching reactions at layer interfaces. Preferably, this layer promoteselectron mobility and reduces quenching reactions. Examples of electrontransport materials for optional layer 140 include metal chelatedoxinoid compounds, such as tris(8-hydroxyquinolato)aluminum (Alq₃);cyclometallated iridium complexes with phenyl-pyridine ligands havingfluorine-containing substituents, such as those disclosed in copendingapplication Ser. No. 09/879014; phenanthroline-based compounds, such as2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (DDPA) or4,7-diphenyl-1,10-phenanthroline (DPA); and azole compounds such as2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and3-(4-biphenylyl)-4-phenyl-5-(4-t-butylphenyl)-1,2,4-triazole (TAZ).

Optional layer 140 can also be made with polymeric materials. Examplesinclude poly(fluorene-oxadiazole), as disclosed in copending applicationSer. No. 09/546512, and some polyphenylenevinylene polymers (PPV), suchas cyano-substituted PPV.

It is known to have other layers in organic electronic devices. Forexample, there can be a layer (not shown) between the conductive polymerlayer 120 and the active layer 130 to facilitate positive chargetransport and/or band-gap matching of the layers, or to function as aprotective layer. Similarly, there can be additional layers (not shown)between the active layer 130 and the cathode layer 150 to facilitatenegative charge transport and/or band-gap matching between the layers,or to function as a protective layer. Layers that are known in the artcan be used. In addition, any of the above-described layers can be madeof two or more layers. Alternatively, some or all of inorganic anodelayer 110, the conductive polymer layer 120, the active layer 130, andcathode layer 150, may be surface treated to increase charge carriertransport efficiency. The choice of materials for each of the componentlayers is preferably determined by balancing the goals of providing adevice with high device efficiency.

The device can be prepared by sequentially depositing the individuallayers on a suitable substrate. Substrates such as glass and polymericfilms can be used. In most cases the anode is applied to the substrateand the layers are built up from there. However, it is possible to firstapply the cathode to a substrate and add the layers in the reverseorder. In general, the different layers will have the following range ofthicknesses: inorganic anode 110, 500–5000 Å, preferably 1000–2000 Å;optional hole transport layer 120, 50–2500 Å, preferably 200–2000 Å;photoactive layer 130, 10–1000 Å, preferably 100–800 Å; optionalelectron transport layer 140, 50–1000 Å, preferably 200–800 Å; cathode150, 200–10000 Å, preferably 300–5000 Å.

EXAMPLES

The following examples illustrate certain features and advantages of thepresent invention. They are intended to be illustrative of theinvention, but not limiting. All percentages are by weight, unlessotherwise indicated.

Examples 1–2

These examples illustrate the formation of a functionalized polymer.

Materials

CN-PPV is a cyano-derivative of poly(phenylene-vinylene). It is similarto that described in Gang Yu and Alan J. Heeger, J. Applied Physics 78,4510 (1995).

Green PPV and other PPVs are derivatives of poly(phenylene-vinylene)similar to those described in D. M. Johansson, G. Srdanov, G. Yu, M.Theander, O. Inganas and M. R. Andersson, “Synthesis andCharacterization of Highly Soluble Phenyl-SubstitutedPoly(p-phenylenevinylene)”, Macromolecules 33, 2525 (2000).

C60 is a fullerene molecule, which was purchased from BuckyUSA Inc.,Florida. PCBM[6,6] is a fullerene derivative with functional side chain,which was synthesized following the procedure published in Iterature [J.C. Hummelen, B. W. Knight, F. Lepec, and F. Wudl, J. Org. Chem. 60, 532(1995)]. Details on its physical properties can be found in N. S.Sariciftci and A. J. Heeger, Intern. J. Mod. Phys. B 8, 237 (1994).

PFO is a poly(fluorene-oxadiazole), which was prepared from thefluorene-dicarboxylic acid, as follows:

Synthesis of 9,9-di-(2-ethylhexyl)-fluorene-2,7-dicarboxylic acid

7 g of magnesium was placed in a 500 ml flask and preheated to 100° C.under dry nitrogen. 5 mg of iodine was added, followed by the first partof a solution (20 ml) of 50 g of2,7-dibromo-9,9-di-(2-ethylhexyl)-fluorene in 100 ml of dry THF. Afterthe reaction was initialized (as indicated by the disappearance of colorfrom the solution), the remainder of the solution was added dropwisewith a syringe. After the addition, the reaction mixture was refluxedfor 1 hour and an additional 100 ml of dry THF was added. The reactionmixture was then cooled to room temperature. 500 g of dry ice was addedto the reaction mixture, and the flask was shaken until the dry ice waswell mixed. After the excess amount of dry ice had evaporated, 800 ml of18% hydrochloric acid was added to the residue. The acidified residuewas extracted three times by ethyl acetate (3×200 ml). The organiclayers were combined and washed with 400 ml water and then dried overMgSO₄. After evaporation of the solvents, 200 ml of hexane was added.The product precipitated as a white solid which was isolated byfiltration. Further purification by recrystallization from methanolafforded 25 g of product as a white solid. The yield of product was 57%.

Proton NMR verified the following structure:

¹H-NMR (500 MHz, THF-d₈) δ in ppm: 8.17 (t, J=6.5 Hz, 2H, fluorenering), 8.06 (d, 2H, J=8 Hz, fluorene ring), 7.89 (d, J=8 Hz, 2H,fluorene ring), 2.13 (d, J=5 Hz, 4H, H-alkyl), 0.65–0.95 (m, 22H,H-alkyl), 0.45–0.54 (m, 8H, H-alkyl).Synthesis of poly(9,9-di-(2-ethylhexyl)-fluorene-oxadiazole)

3.0 g of phosphorus pentoxide was dissolved in 50 ml of methylsulfuricacid with stirring in 110° C. oil heating bath under the protection ofnitrogen. A mixture of 2.0 g of9,9-di-(2-ethylhexyl)-fluorene-2,7-dicarboxylic acid and 286 mg ofhydrazine hydrochloride was added to the solution. The suspension wasstirred over 5 hours and a homogenous, viscous solution was formed.After the solution had cooled to room temperature, the solution waspoured into 500 ml of water. The polymer was precipitated as a whitefiber which was isolated by filtration. The crude polymer was washed byan aqueous solution of sodium carbonate, then water, then methanol, anddried at room temperature in vacuo. The crude polymer was dissolved in25 ml of THF. The solution was filtered through a 5 μm filter, and thepolymer was then precipitated from water. The polymer was isolated andwashed by water, then methanol, and vacuum dried at room temperature.This purification process was repeated three times and afforded thepolymer as a white fiber. The yield of the product was 1.5 g (78%).

Proton NMR verified the following structure:

¹H-NMR (500MHz, THF-d₈) δ in ppm: 8.42 (s, 2H, fluorene ring), 8.26 (d,2H, fluorene ring), 8.13 (d, J=8 Hz, 2H, fluorene ring), 2.2–2.5 (br,4H, H-alkyl), 0.8–1.1 (br, 16H, H-alkyl), 0.59–0.65 (br, 14H, H-alkyl).

Example 1

An amine functionalized acrylic copolymer to be used for subsequentattachment of fused aromatic compounds for the hole transport wasprepared using the following procedure:

To a clean reaction vessel were added:

Step I Amount (grams) Isobutyl methacrylate (IBMA) 21.812-(Tertiarybutylamino) Ethyl Methacrylate(IBAEMA) 18.94 Acetone 250.25

The resulting solution was heated to reflux temperature and held there,with stirring.

The following two solutions, previously mixed for 15 minutes undernitrogen, were then simultaneously added:

Amount (grams) Step II -- Solution (A) Acetone 176.63 Vazo ® 52 catalyst2,2′-azobis(2,4-dimethylpentane nitrile) 14.78 Step III -- Solution (B)Isobutyl methacrylate (IBMA) 196.24 2-(Tertiarybutylamino) EthylMethacrylate 170.46 (IBAEMA)

Solution (A) was fed so that 54.8% was added over a 90 minute period and45.2% over a 330 minute period; solution (B) was fed so that 67% wasadded over a 120 minute period and 33% over a 120 minute period. Afterfeeds were completed, the reaction mass was held at reflux temperaturewith stirring for 120 minutes. A portion of the polymer solution (250grams) was dried in a vacuum oven overnight after evaporating most ofthe solvent using nitrogen sweep. The polymer yield of IBMA/IBAEMA was100%.

Example 2

An hydroxyl functionalized acrylic copolymer to be used for subsequentattachment of fused aromatic compounds for the hole transport wasprepared using the following procedure:

To a clean reaction vessel were added:

Step I Amount (grams) Acetone 600.0

The resulting solution was heated to reflux temperature and held there,with stirring.

The following two solutions, previously mixed for 15 minutes undernitrogen, were then simultaneously added:

Amount (grams) Step II -- Solution (A) Acetone 176.63 Vazo ® 52 catalyst2,2′-azobis(2,4-dimethylpentane nitrile) 4.5 Step III -- Solution (B)Methyl Methacrylate (MMA) 540.0 2-Hydroxyethyl Methacrylate (HEMA) 180.0

Solution (A) and (B) were fed uniformly for 330 minutes and 240 minutesrespectively. After feeds were completed, the reaction mass was held atreflux temperature with stirring for 60 minutes. A portion of thepolymer solution (250 grams) was dried in a vacuum oven overnight afterevaporating most of the solvent using nitrogen sweep. The polymer yieldof HEMA/MMA was 100%. The molecular weight was measured by GPC. Thenumber average (Mn), and the weight average molecular weight were 30,308and 93,195 respectively, to give polydispersity (P_(d)) of 3.07.

Examples 3–4

These examples illustrate the attachment of a fused aromatic ring to afunctionalized polymer.

Example 3

This example illustrates the attachment of a naphthyl ring to thefunctionalized polymer of Example 2.

To a clean, oven dried reaction vessel were added:

Step 1 Amount (grams) HEMA/MMA copolymer from Example 2 20.0Tetrahydrofuran (THF), anhydrous 444.5

The resulting solution was stirred at room temperature under argon untilthe polymer was completely dissolved.

The following reagent was next added in a single portion:

Step 2 Amount (grams) 1,1′-Carbonyldiimidazole (CDI) 7.50

The resulting solution was stirred at room temperature under argon forone hour.

The following solution was then added in dropwise fashion over 20minutes:

Step 3 Amount (grams) 1-(1-Naphthyl)ethylamine 7.90 Tetrahydrofuran(THF), anhydrous 66.7

The resulting solution was stirred at room temperature under argon for48 hours. The solution was then concentrated in vacuo to ⅓ of itsoriginal volume. The concentrated solution was poured into a largevolume of water (200 ml) and the resulting precipitate was collected byfiltration. The crude polymer product was extracted five times withwater (200 ml) in a blender and was then oven dried in vacuo at 50° C.for 48 hours. Polymer yield was 84% by weight.

The polymer was characterized as having the Formula I below:

¹H NMR (DMSO-d₆): δ=6.7–8.1 (aromatic protons for pendant naphthylenegroup); ratio of aromatic H:aliphatic H=0.20 (theoretical=0.19); UV-vis(DMSO): λmax=305 nm

The polymer molecular weight was not measured, as it should be verysimilar to that of the unmodified polymer.

Example 4

This example illustrates the attachment of a pyrene group to thefunctionalized polymer of Example 1.

To a clean, oven dried reaction vessel were added:

Step 1 Amount (grams) 1-Pyrenecarboxylic acid 2.25 Thionyl chloride 90.2

The resulting solution was heated to reflux for two hours. The remainingthionyl chloride was then removed by distillation giving a crude yellowsolid. The solid was washed repeatedly with dry hexanes and then driedin vacuo at 50° C. for 12 hours. Yield of 1-pyrenecarbonyl chloride was95%.

To a second clean, oven dried reaction vessel were added:

Step 2 Amount (grams) IBMA/IBAEMA copolymer from Example 1 10.0Tetrahydrofuran (THF), anhydrous 147.8

The polymer solution was stirred at room temperature under argon untilthe polymer was completely dissolved. The product prepared from Step 1was then added.

The resulting solution was stirred under argon for 12 hours at roomtemperature. The solution was further modified:

Step 3 Amount (grams) Triethylamine 2.93

The resulting solution was stirred under argon for 5 minutes. Thesolution was further modified:

Step 4 Amount (grams) Cyclohexanoyl chloride 2.26

The resulting solution was stirred at room temperature under argon for12 hours. The solution was then concentrated in vacuo to ½ of itsoriginal volume. The concentrated solution was poured into a largevolume of water (300 mL) and the resulting precipitate was collected byfiltration. The crude polymer product was extracted five times withwater (200 mL) in a blender and was then oven dried in vacuo at 50° C.for 48 hours. Polymer yield was 79% by weight.

-   -   UV-vis (DMSO): λmax=340 nm        The polymer molecular weight was not measured as it should be        very similar to that of the unmodified polymer.

Example 5

This example illustrates the preparation of a hole transport of theinvention from functionalized monomers.

A polyaramide having pendant pyrene groups to be employed as a holetransport material was prepared in a multi-step manner as follows:

To a clean, oven dried reaction vessel were added:

Step 1 Amount (grams) 1-Pyrenecarboxylic acid 4.07 Thionyl chloride163.1

The resulting solution was heated to reflux for two hours. The remainingthionyl chloride was then removed by distillation giving a crude yellowsolid. The solid was washed repeatedly with dry hexanes and then driedin vacuo at 50° C. for 12 hours. Yield of 1-pyrenecarbonyl chloride was95%.

The 1-pyrenecarbonyl chloride was further modified. To a clean, ovendried reaction vessel were added:

Step 2 Amount (grams) 5-Aminoisophthalic acid 3.03 N,N-Dimethylacetamide(DMAC) 93.7

The resulting solution was stirred at room temperature under argon. Thefollowing solution, previously mixed for 5 minutes under argon, was thenadded dropwise over 15 minutes:

Step 3 Amount (grams) 1-Pyrenecarbonyl chloride 4.16N,N-Dimethylacetamide (DMAC) 46.9

The resulting solution was stirred at room temperature under argon foreight hours. The DMAC solvent was then removed by vacuum distillation,giving a crude tan solid. The solid was twice washed in methanol andthen dried in vacuo at 50° C. for 24 hours. Product yield was 92%.

The product isolated from Step 3 was further modified using a pyrenediacid having Formula II, below.

To a clean, oven dried reaction vessel was added:

Step 4 Amount (grams) Compound of Formula I 4.50 Thionyl chloride 326.2

The resulting solution was heated to reflux for 12 hours. The remainingthionyl chloride was then removed by distillation giving a crudeyellow-green solid, having Formula III below.

The solid was washed repeatedly with dry hexanes and then dried in vacuoat 50° C. for 12 hours.

The pyrene-diacid chloride of Formula II was then used to make the holetransport polymer. To a clean, oven dried reaction vessel was added:

Step 5 Amount (grams) Compound of Formula II 2.0 1,3-Phenylenediamine0.47 N,N-Dimethylacetamide (DMAC) 37.5

The resulting solution was stirred at room temperature under argon for12 hours. The solution was then poured in water giving a yellow-tanprecipitate. The precipitate was collected and extracted with methanol.The resulting polyaramide was dried in vacuo at 50° C. for 48 hours.Polymer yield was 81% by weight.

The polymer was characterized as having Formula IV below:

¹H NMR (DMSO-d₆): δ=11.1–11.3 (m, 1 H); 10.6–10.7 (s, 2H); 7.9–8.7 (m 16H). UV-vis (DMSO): λmax=345 nm. Inherent viscosity (0.5 wt %, H₂SO₄, 25°C.)=0.61 dL/g.

Example 6–12

These examples illustrate the use of the polymers of the invention intwo-terminal, thin film devices.

Example 6

The polymer layer was sandwiched between two conductive electrodes madeof inorganic metals or organic conductive polymers. One set of deviceswas made as follows. A 1000 Å gold layer was thermally evaporated ontoglass substrates. A conductive layer of poly(3,4-ethylenedioxythiophene)(PEDOT) was then coated on top. The Au/PEDOT layer formed the anode 110of this device. Polymer from Example 5 was coated from 2% solution indimethylacetamide (DMAC) filtered through a 0.45 μpp filter. Thethickness of resulting film was ˜500 Å, which was measured by a TENCOR500 Surface Profiler. The cathode electrode was a Ba(30 Å)/Al(3000 Å)bilayer structure, which was vapor deposited on top of the active layersunder a vacuum of about 3×10⁻⁶ torr. The active area of the device wasdefined by the two electrodes, and was ˜0.15 cm² in this experiment.Device performance was tested inside a dry box using a Keithley 236Source-Measure-Unit.

The current vs voltage (IV) characteristics are shown in FIG. 2. Thistwo-terminal device had a good rectification effect. Curve (200) plotsthe current when a reverse bias is applied, while curve (210) plots thecurrent when a forward bias is applied. At a forward bias of 15 V, theforward current was 50 mA (330 mA/cm²), 5000 times higher than thecurrent under −5 V bias. Such a device can be used as an electricswitch. When the “ON” state is defined at 14 V bias, and the “OFF” stateat zero bias, the switch ratio (I_(on)/I_(off)) is larger than 10⁷.

Similar devices were prepared using Au, Pt, Ag, Ni, Cu, Se, polyaniline(PANI), and polypyrrole as the anode electrode. Similar results wereobserved. Similar devices were prepared using Ba, Li, Ce, Cs, Eu, Rb, SmAl, In, LiF/Al, BaO/Al and CsF/Al as the cathode electrode, and similarI-V characteristics were observed.

This example demonstrates that the polymers disclosed in this inventioncan be used to fabricate two-terminal, thin film devices with goodrectification effect. Such devices can be used as solid state electricswitches.

Example 7

Devices were fabricated with the same material and with a similarprocedure as given in Example 6. In this case, the cathode and anodeelectrode were patterned with shadow masks. 10×10 diode arrays werefabricated. The pitch size of each pixel was 0.3 mm, which was definedby the widths of two contact electrodes. The I-V characteristics of eachpixel were analyzed, and behavior similar to that shown in FIG. 1 wasobserved.

This example demonstrated that the polymers disclosed in this inventioncan be used to fabricate microswitch arrays.

Example 8

Devices were fabricated using a procedure similar to that given inExample 6. In this case, the active polymer was the polymer from Example3. THF was used as the solvent. The I-V characteristics were similar tothat of Example 6. The device forward current reached 330 mA/cm² at ˜20V.

This example, as well as Example 6, demonstrates that the polymers ofthe invention can be used as the active layer for two-terminal switchingdevices.

Example 9

Thin film light emitting devices were fabricated following the proceduredescribed in Example 6. In these devices, a transparent ITO electrodewas used as the anode (Layer 110 as best seen in FIG. 1). A layer ofpoly(vinylcarbazole) was used as the hole transport layer (Layer 120 asbest seen in FIG. 1). On top of this layer, the polymer from Example 4was applied as the EL layer (Layer 130 as best seen in FIG. 1). It wasspin coated from THF solution, using a procedure similar to thatdescribed in Example 8. The resulting thickness of the film was about950 Å. Ba and Al layers were vapor deposited on top of the EL layerunder a vacuum of about 3×10⁻⁶ torr. The thicknesses of the Ba and Allayers were 30 Å and 3000 Å respectively. Device performance was testedinside a dry box using a calibrated Si photodiode and a Keithley 236Source-Measure-Unit.

FIG. 3 shows the current versus voltage (“I-V”) (curve 230) and lightemission versus voltage (“L-V”) (curve 240) characteristics of thisdevice. Blue light emission was observed in forward bias. The emissionwas ˜50 cd/m² at 40V. The external quantum efficiency was 0.2% ph/el ina broad voltage range. EL emission spectrum revealed that the emissionwas from the polymer disclosed in Example 4 (by comparison with thephotoluminescent spectrum of the same material.

Devices were also fabricated in similar configuration but with a PEDOTlayer (˜1000 Å) in between ITO and PVK layer. The performance parametersof these devices are similar to that shown in FIG. 3.

This example demonstrated that the polymers disclosed in this inventioncan be used as the light emitting material in polymer light emittingdevices.

Example 10

Thin film light-emitting devices were fabricated following the proceduredescribed in Example 9. In these devices, ITO was used as the anode(Layer 110). A layer of polymer from Example 5 was used as the holetransport layer (120). Over the hole transport layer, ˜1000 Åpoly(fluorene-oxadiazole) (PFO) was spin-coated (layer 130). Ca/Al wasused as the cathode electrode (150). Blue light emission characteristicof PFO was observed with an external quantum efficiency ˜1% ph/el. TheCIE color coordinates were x=0.18, y=0.15, which was close to thenumbers recommended by the CIE for color display applications. Thesedevices could be operated at low bias voltage. Light emission wastypically observed above 4 volt, reaching ˜100 cd/m² at ˜8 V and over10³ cd/m² at 10V.

The procedure was repeated with a poly(phenylene vinylene) derivativewith alkyl side chains as the layer 130. Green light emission wasobserved for voltages larger than 4V with EL efficiency of 5–10 cd/A.

The procedure was repeated with a poly(phenylene vinylene) derivativewith alkoxy side chains as layer 130. Orange-red light emission wasobserved for voltages larger than 4 V, with an EL efficiency of 2–3cd/A.

This example demonstrates that the polymers disclosed in this inventioncan be used as the hole transport materials for blue, green and redlight emitting devices. Such devices can be used as the pixels infull-color emissive displays.

Comparative Example A

Experiments were carried out following the same procedure as describedin Example 10, but using PVK (Sigma-Aldrich, Milwaukee, Wis.) as thehole transport layer (120). Results similar to those described inExample 10 (with a hole transport polymer disclosed in this invention)were observed.

This example, along with example 10, demonstrates that the polymersdisclosed in this invention can be used as the hole transport materialsfor blue, green and red light emitting devices. Such devices can be usedas the pixels in full-color emissive displays.

Example 11

Thin film devices were fabricated in configuration of ITO/polymer fromExample 5 (100 nm)/Ba (3 nm)/Al (100 nm). The current voltagecharacteristic under white lamp illumination was measured. Aphotovoltaic effect was observed under UV illumination. The open circuitvoltage was ˜2V. The photosensitivity at 336 nm was approximately 1mA/Watt.

This example demonstrates that the polymers disclosed in this inventioncan be used to fabricate photodetectors for ultraviolet light detection.

Example 12

The procedure of Example 11 was repeated, but with an active layer madeof polymer blends containing the polymers of Examples 3 and 5, and anadditional polymer or molecule with a smaller optical energy gap. Thephotoresponse was measured for these devices. The table below providesthe range of spectral response obtained from this blend.

Additive Spectral range PFO 400 nm Green PPV derivative 500 nm CN-PPV600 nm C60, PCBM[6,6] 710 nm

This example demonstrates that the polymers disclosed in this inventioncan be used as host materials for the fabrication of photodetectors withdifferent spectral response ranges. Blends with response to nearinfrared or infrared spectral range are also suitable for energyconversion devices such as solar cells.

1. A hole transport polymer comprising a polymeric backbone havinglinked Thereto a plurality of substituents, said substituents comprisingat least one fused aromatic ring group, with the proviso that thepolymer does not contain groups selected from triarylamines groups andcarbazole groups wherein the polymeric backbone is selected frompolyaramides, polystyrenes, polyarylenes, polyesters, polyvinyl ethersand polyvinyl esters.
 2. The hole transport polymer of claim 1 whereinthe fused aromatic ring groups are selected from naphthyl, anthracyl,phenanthryl, phenalenyl, fluorenyl, pyrenyl. tetracenyl and pentacenylgroups.